New York Natural Heritage Program
Cerulean Warbler
Setophaga cerulea (Wilson, 1810)

General Description [-]
The Cerulean Warbler is a small passerine that weighs approximately 8-10 grams. Males are sky blue in color, with a black necklace.

Identifying Characteristics [-]
The best identifying features are the cerulean blue plumage on their head and back and black "necklace" on males. Males are also white underneath with streaking on their sides. Cerulean Warblers have a relatively short tail, and in all plumages, both sexes display two white wing bars. Females are often difficult to see during the breeding season and are also more difficult to identify. They have a dull bluish-green-grey tinted head and back and a cream-colored eyestripe. Females are yellowish underneath with light dusky streaking on their sides. The male's song is an accelerating series of buzzy notes followed by a longer higher-pitched trill-like note. It is sometimes described as "zee-zee-zee-tititi-zeee". Their song is distinctive but could be confused with Black-throated Blue Warbler, Northern Parula, or Blackburnian Warbler.

Characters Most Useful for Identification [-]
The best identifying features for males are the cerulean blue plumage on their head and back and black necklace.

Best Life Stage for Proper Identification [-]
Breeding season adults, especially males, are easiest to identify.

Behavior [-]
Cerulean Warbler males are highly territorial during the breeding season and maintain territories averaging roughly 0.74-2.5 acres (0.3-1.0 ha) in size (Buehler et al. 2013). They tend to exhibit clustered territoriality, meaning that territories occur together in groups rather than evenly distributed within the habitat. It is not clear whether this is due to conspecific attraction, the tendency for individuals of the same species to settle near one another, or to limited availability of quality habitat; there is some evidence that both may be factors (Roth and Islam 2007).

Cerulean Warblers forage by gleaning insects from leaves and twigs usually beginning at the proximal part of a branch and hopping along towards the distal end (Buehler et al. 2013). They forage mostly in the forest canopy at the mid-canopy level (George 2009; Wood and Perkins 2012). They are vigorous singers and often sing from song posts within the canopy or upper-canopy (Barg et al. 2006; George 2009; Wood and Perkins 2012).

Cerulean Warblers are typically monogamous for the breeding season (Buehler et al. 2013) and both males and females may select nest locations (Oliarnyk and Robertson 1996; Boves and Buehler 2012). They raise a single brood but will renest if a nest fails (Hamel 2000).

Diet [-]
Cerulean Warblers are insectivores. There are no published studies of their specific diet in New York. Research on this subject is not extensive; however a few studies in other states found that Cerulean Warblers consumed primarily Homoptera and larval Lepidoptera (Howell 1924; Hamel 1992; Sample et al. 1993), as well as Coleoptera and Hymenoptera (Hamel 1992; Sample et al. 1993).
The Best Time to See
The Cerulean Warbler is present in New York during their spring and summer breeding season and also passes through during migration. The best time to see them is anytime from spring migration through the late summer when their plumage is most recognizable. Males sing most strongly in the spring for the first few weeks after arrival on their breeding grounds in late April to mid-May. The website reports high frequencies of Cerulean Warblers on checklists in New York submitted from May 1st through the first two weeks of June (eBird 2013).
Present Breeding
The time of year you would expect to find Cerulean Warbler present (blue shading) and breeding (orange shading) in New York.